Evaluation of Transmission and Quality Performance of Digital Secure Voice Communications in an HF Network

High-grade narrowband speech security for high frequency (HF) transmissions can be achieved using low rate speech coders and encryption algorithms. This paper presents test results for an HF channel and the structure of a test system that uses a mixed excitation linear prediction (MELP) vocoder for digital plain and secure speech transmission. The system is tested for bit error percentage in the received MELP bitstream, for its spectrum characteristics and with a perceptual evaluation speech quality (PESQ) test for synthetic speech under a number of different test conditions. In this paper, the transmission performance of the digital secure speech is analyzed first, and then the speech quality performance is assessed according to the HF channel distortions. As far as could be determined from the literature, this study represents the comprehensive performance analysis of digital secure speech transmission over HF channels. The results of this study may be used to design a technique for efficient, secure communication over an HF network.